Without limiting the scope of the invention, its background is described in connection with applications of thin-film ferroelectric and pyroelectric materials.
The class of materials known as the perovskites exhibit several properties which make them useful in the microelectronics industry. Among these properties is a dielectric constant which can be several orders of magnitude greater than that of conventional insulators used in integrated circuits (e.g. SiO.sub.2 and Si.sub.3 N.sub.4). This high dielectric constant can allow fabrication of very small capacitors which store charge in conventional DRAMs (dynamic random access memories), thereby increasing the density of memory cells.
Related to the dielectric constant is the pyroelectric figure of merit (pyroelectric FOM). The pyroelectric FOM is proportional to the ratio between the pyroelectric coefficient and dielectric constant. The pyroelectric coefficient is a function of the dielectric constant and the spontaneous polarization. Many perovskites exhibit a very large pyroelectric FOM, and if sufficiently large this pyroelectric property makes possible devices which are very sensitive to changes in temperature, including temperature changes caused by impinging electromagnetic radiation. Arrays of such pyroelectric detectors are now being fabricated which can image an infrared scene. These detectors do not require cryogenic cooling and are therefore economically feasible for consumer applications.
The ferroelectric properties of perovskite materials are also useful in the microelectronics industry. Among those properties is the remanent polarization. The direction of this polarization may be switched by the application of an electric field to the material. The direction of this polarization may then be sensed electronically. The remanent polarization of these materials suggests that FRAMs (ferroelectric random access memories) could be constructed which would be non-volatile, i.e. the state (logic one or zero) of each memory element would be retained even if power is removed. Such devices, depending on the configuration, could in addition exhibit faster read/write cycles than conventional DRAMs.